Abstract
We studied three active regions (NOAA 10030, 10069, 9661), which produced large flares. We analyzed the time evolution of the magnetic helicity injection Hin and force-free parameter &aipha; on flare days. We employed two kinds of data: One is the low cadence data (90 min) of longitudinal magnetograms of the full disk obtained from SOHO/MDI and vector magnetograms obtained by the Solar Flare Telescope (SFT) at National Astronomical Observatory of Japan. The other is the high cadence data (10 min) made from the interpolated SOHO/MDI magnetograms and the averaged SFT magnetograms. The results indicate that the temporal variation of the accumulated helicity injection roughly follows the time variation of force-free parameter α.
